EGR valves may be used in engines to recirculate part of the exhaust gas back into the internal combustion chamber of the engine. This has the benefit of lowering the emissions of the engine and therefore lowering the emissions of the vehicle in which the engine is situated, since the presence of exhaust gas dilutes the oxygen percentage in the incoming air stream with gases inert to combustion which therefore absorb heat. This may have the effect of lowering the engine temperature and therefore reducing the amount of NOx gases generated, since NOx gases are generated when nitrogen and oxygen are subject to high engine temperatures.
As EGR valves recirculate exhaust gas they may be prone to accumulating carbon deposits and other particulates in the exhaust gas that can hamper, or prevent, the valves from opening. Without treatment (e.g. cleaning or other maintenance) this can eventually lead to the EGR valve sticking closed, fully open, or partially open. For example, EGR valves of the poppet design can suffer from contamination of the valve stem which, as above, can lead eventually to the valve sticking closed, fully open, or partially open. Before EGR valves become fully stuck they may exhibit slow movement demanding large control effort and may exhibit jerky “stick-slip” motion. This can result in too much or too little exhaust gas flowing, which can lead to undesirable engine operations including increased engine-out emissions, combustion instability, inefficient engine starting, overheating of engine components, etc.
If this is detected by the diagnostic elements of the engine control system then this may result in a reduction in the engine power, or even the engine being disabled. Consequently, the vehicle may demand a visit to a repair facility, which may include replacement of the EGR valve depending on a magnitude of the contamination.
EGR valve contamination may be caused by, for example, the condensation of hydrocarbons and water and the accumulation of soot onto the EGR valve stem, which may be exacerbated at low temperatures. Increased usage of EGR valves at low temperatures due to more stringent emissions standards may be more likely to increase the risk of the above described type of “cold fouling” and/or “cold contamination” of the EGR valve.
In one example, the issues described above may be addressed by a method for comprising executing an EGR valve diagnostic following an engine deactivation, wherein the EGR valve diagnostic calculates three or more of a breakaway value, a holding power value, a hang time value, a travel time value, and a travel speed value as an EGR valve is actuated from a resting position, to a predetermined position, and back to the resting position. In this way, an estimation of a contamination and/or an accumulation of particles on the EGR valve may be gathered, which may signal an EGR valve cleaning mode to block the EGR valve from becoming too contaminated such that service is requested.
As one example, the breakaway value, holding power value, hang time value, travel time value, and travel speed value are compared to respective thresholds, wherein if one or more of the values is outside of its respective threshold, then the cleaning of the EGR valve may be signaled. The EGR valve diagnostic may function to determine when EGR valve operation has degraded. However, this degradation may be relatively small such that engine operating characteristics are not impacted by the degraded EGR valve operation. As such, the EGR diagnostic may be a preventative diagnostic used to estimate when contamination of the EGR valve is sufficient to demand the cleaning, which may occur in response to a measured characteristic of the EGR valve not meeting a desired value.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.